HOUSTON (Reuters) - U.S. drug enforcement agents and Los Angeles police on Wednesday raided a Houston clinic owned by Conrad Murray, the doctor who was with pop icon Michael Jackson when he died, looking for evidence of manslaughter.

Agents with the U.S. Drug Enforcement Administration entered the Armstrong Medical Clinic in north Houston to serve a search warrant in an effort to help Los Angeles police probing the death of the "Thriller" singer, said Rusty Payne, a Washington-based spokesperson for the agency.

The Los Angeles Police Department's homicide division was involved in the search, and the warrant authorized them to "search for and seize items, including documents, they believed constituted evidence of the offense of manslaughter," said Ed Chernoff, Murray's lawyer.

Payne declined to give details because the Texas search warrant remained sealed.

A Los Angeles police spokeswoman confirmed that their detectives served the warrant with the assistance of the DEA, but declined to say what investigators were looking for.

One law enforcement official, who declined to be named, said the focus of the search was propofol, an anesthetic also known as Diprivan, which has repeatedly been named in media reports as a drug Jackson was said to be taking before he died on June 25.

Murray's clinic -- a nondescript building in northeast Houston flanked by a liquor store and a convenience store -- was swarmed by television broadcast trucks, and helicopters hovered overhead.

Agents left the office soon after noon with a forensic image of a business computer hard drive and 21 documents, Chernoff said in a statement.

"They cooperated fully," a Houston Police Department officer told a crowd of reporters and other onlookers that stood outside in the summer heat. "They want everybody to go, please."

JACKSON'S DRUG USE

Jackson, 50, died of cardiac arrest at his rented Los Angeles mansion just a few weeks before a planned string of 50 comeback concerts in London.

Since then investigators from several California agencies and federal DEA officials have focused their probe into the cause of death on the singer's prescription drug use and doctors who may have provided the drugs to Jackson.

Los Angeles officials have repeatedly declined to confirm those reports, and an official cause of death is pending results of toxicology tests.

A spokesman for the Los Angeles coroner's office, which is one of the agencies looking into Jackson's death, said a report should be released at the end of next week, but he declined to comment on whether a cause of death had been determined.

He said the coroner's office was not involved in the Houston raid.

Murray, who was hired to be Jackson's personal physician ahead of the London concerts, has told police he did not inject the singer with painkillers before his cardiac arrest.

After questioning Murray back in June, Chernoff's law firm issued a statement saying at the time, that "Investigators say the doctor is in no way a suspect and remains a witness to this tragedy."

(Additional reporting by Anna Driver in Houston, James Vicini in Washington and Alex Dobuzinskis in Los Angeles, Editing by Sandra Maler and Bob Tourtellotte)

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